The cycle duration of the seminiferous epithelium remains unaltered duringGnRH antagonist-induced testicular involution in rats and monkeys

Although the gonadotropic control of the spermatogenic process is well esta blished, the endocrine regulation of the timing and kinetics of germ cell d evelopment has received little attention. We found previously that the admi nistration of a GnRH antagonist (ANT) over a period of 25 days could retard spermatid development and slightly prolong cycle length in intact adult cy nomolgus monkeys (Macaca fascicularis). The aim of the present study was to investigate the effects of extended exposure to ANT on the duration of the cycle of the seminiferous epithelium in the monkey. Additionally, the dura tion of spermatogenesis was studied in the ANT-exposed rat model. In experi ment 1, monkeys were given either saline or ANT (n=6/group) and on day 30 a ll animals received a single injection of 5-bromodeoxyuridine (BrdU) to lab el S-phase germ cells. Testicular biopsies were taken on days 39, 43, 17 an d 51 tend of treatment) for BrdU localization and flow cytometric analysis. ANT treatment suppressed hormone levels, reduced testis size by >70% and s everely impaired germ cell production. Despite these alterations, cycle dur ation remained unchanged at all time-points compared with controls (10.12 /- 0.15 days vs 10.16 +/- 0.44 days). In experiment 2, adult male Sprague-D awley rats (n=15/group) received either vehicle (VEH) or ANT for 14 days an d received BrdU injection on day 2. Cycle duration was found to be shorter in the ANT-treated group (12.45 + 0.09 days) than in the control group (12. 75 +/- 0.08, P<0.05). As spermatogenic cycle length in this control group w as longer than that of our historical controls (range: 12.37-12.53 days), e xperiment 2 was repeated (n=10/group). In experiment 3, cycle duration was 12.51+/-0.02 for VEH and 12.46+/-0.05 for the ANT-treated group (P>0.05) in both species. We concluded that the duration of the cycle of the seminifer ous epithelium in monkeys and rats is independent of gonadotropins but is r ather regulated by the spermatogenic tissue itself.